Domain Wall MRAM Initialization via Pinning Sites

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Solution Overview

Problem

Domain wall motion type MRAMs with perpendicular magnetic anisotropy face challenges in initializing the magnetization state, particularly due to the difficulty in forming a domain wall using external magnetic fields, which leads to high write currents and power consumption.

Innovation Solution

A magnetic recording layer with perpendicular magnetic anisotropy is designed to include pinning sites for domain wall trapping, and a method involving sequential external magnetic fields and current application is used to initialize the magnetization state, allowing for reduced write current and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a domain wall motion type MRAM with perpendicular magnetic anisotropy is used, then write current can be reduced, but initialization of magnetization state becomes difficult

Engineering Contradiction:

Improvewrite currentVSAvoidinitialization of magnetization state

Core Design Contradiction:

Use of energy by moving objectVSEase of operation

Solution Approach 1:

The patent applies preliminary action by introducing a specific magnetic field during the initialization process to pre-establish the desired magnetization state before normal operation. The magnetic field is applied in a predetermined direction to align the magnetization of the ferromagnetic layer, ensuring proper initialization without requiring high write currents during subsequent operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent utilizes parameter changes by varying the magnetic field strength and direction during initialization. A magnetic field with sufficient strength is applied in a specific direction to switch the magnetization state, and then the field is removed or reduced. This dynamic adjustment of magnetic field parameters enables effective initialization while maintaining low operational write currents.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If external magnetic field is used to form domain wall, then magnetization state can be initialized, but write current increases and power consumption rises

Engineering Contradiction:

Improvemagnetization state initializationVSAvoidpower consumption

Core Design Contradiction:

Ease of operationVSUse of energy by moving object

Solution Approach 1:

The patent applies periodic action through a two-stage magnetic field application process. First, a magnetic field is applied to initialize the magnetization state, then the field is removed or reduced. This periodic application and removal of the magnetic field enables initialization while allowing the system to return to a low-power state for normal operation with reduced write currents.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The magnetic field application serves as a preliminary action that prepares the magnetization state before normal write operations. By establishing the correct initial magnetization configuration through this preliminary magnetic field application, the system avoids the need for continuous high write currents, thereby reducing overall power consumption during data writing operations.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The method effectively initializes the magnetization state of the magnetic recording layer with perpendicular magnetic anisotropy, resulting in a low power consumption domain wall motion type MRAM with reduced write current.

Implementation Method 1

a spin-polarized current is injected to a ferromagnetic conductor, and direct interaction between spin of conduction electrons of the current and magnetic moment of the conductor causes the magnetization to be switched (hereinafter referred to as "Spin Transfer Magnetization Switching")

Methodology Applied

Scientific EffectSpin transfer:

Implementation Method 2

a current is so supplied as to pass through the domain wall and the current causes the domain wall to move

Methodology Applied

Scientific EffectCurrent-driven domain wall motion:

Implementation Method 3

a magnetoresistance element that exhibits a "magnetoresistance effect" such as TMR (Tunnel MagnetoResistance) effect is utilized

Methodology Applied

Scientific EffectMagnetoresistance effect: Magnetoresistance

Data Source

PatentUS8174873B2Magnetic random access memory and initializing method for the same

Publication Date: 2012.05.08 NEC CORP

AI summary

A domain wall motion type MRAM has: a magnetic recording layer 10 having perpendicular magnetic anisotropy; and a pair of terminals 51 and 52 used for supplying a current to the magnetic recording layer 10. The magnetic recording layer 10 has: a first magnetization region 11 connected to one of the pair of terminals; a second magnetization region 12 connected to the other of the pair of terminals; and a magnetization switching region 13 connecting between the first magnetization region 11 and the second magnetization region 12 and having reversible magnetization. A first pinning site PS1, by which the domain wall is trapped, is formed at a boundary between the first magnetization region 11 and the magnetization switching region 13. A second pinning site PS2, by which the domain wall is trapped, is formed at a boundary between the second magnetization region 12 and the magnetization switching region 13. A third pinning site PS3, by which the domain wall is trapped, is formed within the first magnetization region 11.